A variety of devices that detect an abnormality of a secondary battery on the basis of variations in battery properties during repeated charging and discharging and long-term storage have been suggested. A device that detects a leakage abnormality of a secondary battery by comparing a variation amount of an internal resistance of a secondary battery caused by charging for a predetermined time with a reference value has been suggested as one of such devices (see, for example, Patent Document 1).
According to the technique described in Patent Document 1, a leakage abnormality that has occurred in a battery is detected by using a battery property such that a variation amount of an internal resistance in the battery having an abnormality becomes larger than that in a normal secondary battery.
However, since the internal resistance of a secondary battery varies in response to a state of charge (SOC), a variation amount of internal resistance caused by charging for a predetermined time differs depending on a SOC at the time the charging has been started, even in a normal secondary battery. The resultant problem is that where an abnormality is detected by comparing a variation amount of an internal resistance of a secondary battery caused by charging for a predetermined time with a reference value, the abnormality is difficult to detect with high accuracy.